1. Field of the Invention
This invention relates to methods for transporting silicon wafers, in particular such methods in which the wafer is aligned, and apparatus which is suitable for use in such methods. It includes the methods and apparatus disclosed in, commonly assigned U.S. application Ser. No. 052,496, filed May 21, 1987, now abandoned, as well as further improvements of that method and apparatus.
2. Introduction to the Invention
In the manufacture of solid state devices, silicon wafers are moved between different work stations, often in cassettes which hold a number of spaced-apart wafers stacked next to each other in pockets. Many processes require that the wafer is precisely aligned. The alignment required may be the precise positioning of the center of the wafer and/or the precise orientation of the wafer relative to its crystalline plane, which is indicated on the wafer by a marker of some kind, usually a flat or notch on the perimeter of the wafer. The transporting of individual wafers (including in particular their removal from cassettes, their placement into cassettes, and their alignment, as well as their simple transport from one location to another) is a matter of vital concern to the semiconductor industry.
Known methods of transporting individual silicon wafers involve contact between (a) the underside of the wafer and (b) solid support surfaces or air jets which are likely to contain solid particles. It is already known that these methods can damage or contaminate the underside of the wafer, but this has not hitherto been a matter for concern. However, it has now been found that these known methods can also damage or contaminate the working surface of the wafer.